A window manufacturer receives a quantity of raw materials into the factory and ships completed windows from the factory on a truck for delivery to a construction site and/or retail sales locations. One component of windows is the insulated glass unit. The insulated glass unit (IGU) consists of one or two spacer frames of metal and two or three (inner, center and outer) glass lites (sometimes referred to as panes) that are adhesively attached to the spacer frame. The completed IGU can be shipped as a completed product to a window manufacturer or can be assembled into a window sash on site at an integrated manufacturer.
Representative prior art patents owned by the assignee of the present invention relating to fabrication of window IGUs are U.S. Pat. No. 6,173,484 B1 to McGlinchy et al, U.S. Pat. No. 5,295,292 to Leopold, and U.S. Pat. No. 5,361,476 to Leopold. The disclosure of these prior art patents is incorporated herein by reference.
In the window and door industry, processing special orders requires a special or separate order, batch or schedule to be created. Certain conditions allow for a special, batch to be generated either at the beginning or end of a schedule, but this severely limits the items that can be placed in the special batch.
If a special schedule is created, this special schedule must be produced separately from the daily production. This requires that items contained in all special schedules be manufactured before or after the daily production schedule.
If the conditions do allow for a special batch to be added to the main daily production schedule, then the special batch will either be manufactured first or last in the daily production
In either the case of a special schedule or a special batch, the glass for the special items is optimized separately in its own glass batch. Using either of the above methods results in every schedule being treated the same.
When using the current methods for creating and handling special items in the window and door industry, less than optimum glass usage can occur. Currently glass lites that need to have a special process performed (i.e. tempering, edge/bevel grinding, shapes, lamination etc) need to have their own separate batch. This reduces a glass optimizer's yield, because optimizers perform their optimization on batches. Once the lites have been cut they are placed in specific glass carts to be transferred to their destination to form part of an integrated glass unit.
The Glass Batch size is normally determined by maximum number of glass slots available in the glass cart(s) to be used for optimization. There are other possible restrictions to racking or slotting of the glass that will reduce the actual number of glass slots available. The following are examples:                Maximum glass thickness allowed per slot: If the glass thickness is greater than the maximum allowed per slot then two slots must be used (allocated) for that lite.        Skip Slot for Triple: When allocating slots the optimizer may presume that in a given batch an empty slot is left after the last lite of triple pane IG Unit(s). This empty slot reduces confusion during the assembly process.        The Optimizer Skips Slots for Out Sourced Lites by leaving an empty slot for pre-cut lites.        
This prior art system can result in a larger glass inventory thus causing extra glass transport and handling systems to be used which increases cost in maintaining the large inventory. In order to keep glass scrap to a minimum, smaller glass sheets are sometimes used. These smaller glass sheets are part of the glass inventory and also take up additional factory floor space.
Multiple starting and stopping of the daily production schedule results in a loss of manufacturing efficiency when special units or items are immediately needed. Special Items are also more easily lost during the manufacturing process.